add startwith check to action method. fix #r343942724

Author: om3rcitak

src/Html/Button.php

@@ -185,7 +185,11 @@ public function actionSubmit()
      */
     public function action($value)
     {
-        $this->attributes['action'] = "function(e, dt, node, config) { $value }";
+        if (substring($value, 0, 8) == 'function') {
+            $this->attributes['action'] = $value;
+        } else {
+            $this->attributes['action'] = "function(e, dt, node, config) { $value }";
+        }
 
         return $this;
     }